Electrical circuits



Oct. 29, 1946.

ELECTRICAL CIRCUIT Filed Aug. 6. 1935 aeciewsn AMPLIFIER- HIGH QF'RE UEM Y j; ELECTRIC GENEEWT'ORQ.

I INVENTOR. Ear/mm M Harrison ATTORN BJM. HARRISON 2,410,065

Patented Oct. 29, 1946 ZAMQS ELECTRICAL CIRCUITS Bertram M. Harrison, Newton, Mass,

by mesne assignments, to

Company, Boston, ware assignor, Submarine Signal Mass, acorporation of Dela- Application August 6, 1935, Serial N 0. 34,938

.6 Claims.

The present invention relates to a system for transmission and reception of compressional waves where the same unit serves both to project the. compressional wave energy and to pick up or receive the energy from the medium after reflection from the object whose distance is being measured or whose position. is being observed.

In systems of this nature it is usually necessary tohave the projecting'and receiving device, which is sometimes called a transceiver, connected to some form of amplifying circuit to amplify the impulses picked up by the projector when used as a pickup unit. Under these conditions if the amplifier remains in circuit with the energizing means operating the unit as a projector, the receiver is apt to be paralyzed or damaged by the power applied to the system.

Various means have been tried to maintain the receiver amplifier in circuit while the power is being applied and at the same time protect them so that the full power of the source is not applied to it. Various means and methods have been used for this purpose, some of which include applying a protective discharge device across the receiver amplifier which breaks down when a large voltage is applied to the projector and which again assume ahigh impedance when the applied voltage has been removed. In other systems relays have been used to shift the connections from sending to receiving after the sending impulse has been delivered.

In these means and methods and in others that have been attempted various difliculties still seem to persist. Either the arrangement is not rapid enough to allow the receiving system to be used soon enough after the impulse has been transmitted or too much energy is consumed either across the source when the system is used for receiving or across the receiver when the system is used for transmitting. In addition to this, in some of the systems the receiver is not sufficiently protected to prevent the receiving circuit from becoming paralyzed for too long a time after the impulse has been emitted.

In the present invention the receiving circuit is at all times connected with the pickup unit and similarly the power supply and. the receiving system is at all times operable immediately after the emitted signal has been given. In addition to this, there is no possibility for the receiver to become paralyzed by the power in the driving or projection-energizing circuit. In this manner immediately after a short signal has been emitted, the system is capable of receiving the reflected echo and therefore very short distances can be measured by the echo system employing the time-of-travel method.

In addition to these advantages the coupling circuit may be tuned to the signal that is being received so that. a selection can be made between the echo of the transmitted signal and other sounds such as extraneous water noises. This applies also in the case of frequencies that may be present in the supply source itself so that the present system provides a remarkably quiet method of listening. 7

With all these advantages it will be noted from consideration of the specification that practically the entire terminal voltage of the projector when used as a pickup unit is impressed across the receiving circuit so that practically one hundred percent efliciency is maintained in the system when used for receiving.

The present arrangement will be more fully described and better understood from a consideration of the description given below in connection with the drawing which shows schematically the invention as applied to depth sounding and sound ranging.

In the drawing I indicates the transceiver which. may be a high frequency oscillator of the magnetostriction or piezo-electric means. The oscillator is in a series circuit with the inductance L1, the capacity C1, which may be variable, and the inductance L2. Shunted across the inductance L2 by the leads 3 and Q is a receiver amplifier unit 5 which may be and preferably is a vacuum tube amplifier of the usual type. The output of the receiver amplifier may be connected by the line 5. and the ground I to an indicating system 8. The indicating system is preferably of the continuous rotating. type in which a shaft 9 is continually rotating, the shaft carrying indicating disc I0 and the cam 20 for operating the transceiver l as a projector. The indicating disc Ill may be provided with an indicating device I I, as, for instance, a neon discharge tube which is connected through to the line 6 through the commutator ring 12 and the brush l3. The other side of the neon light may be grounded as indicated at It.

A scale I5 may be provided with an indicating device, and the cam 28 may be adjusted with reference to the position of the discharge tube on the scale so that thecontacts It and I! may emit a signal by operating the driver or high frequency electric generator IS, the output I9 of which is coupled to the inductance L1 as indicated. When the contacts I6 and I! are closed, thedriver or high frequency electric generator energizes the projector and an impulse is transmitted to the propagating medium which, after reflection from the object whose distance and direction are being observed, returns to energize the transceiver again as a, pickup unit. Thi impulses impresses a potential across the inductance L2 which is connected to the input of the receiver amplifier where it is amplified and then impressed upon the discharge tube I I to produce an indication of distance. By reading the position of the light adjacent to the scale, the distance may be measured.

In the system as described the impedances L1, L2 and C1 must be chosen with reference to the frequency and the impedance of the transceiver to bring about the desired operating conditions. In general the inductance L1 and capacity C1 are chosen so that at the frequency at which the transceiver is operated, the reactive components of these two elements are equal and opposite so that the effective impedance in series is equal to their resistive component.

The impedance of the inductance L2 is chosen at about one-tenth the value of the impedance of L1, but it may be chosen at other values, depending upon the amount of voltage allowable across this inductance when the circuit is being energized by the driver or high frequency electric generator. In general the impedance value of L2 is kept somewhat below the value of the impedance of the transceiver, as under these conditions the circuit appears to have its greatest eihciencyj Since L1 and C1 are tuned to resonance for the frequency that is being transmitted,they will also be in resonance for the frequency at which the transceiver acts as a receiver so that the impedance across the transceiver under these conditions will be made up practically entirely by the impedance of the inductance L2. Under transmitting conditions the Voltage across L2 may be about 40% of the voltage across the transceiver, and under receiving conditions the voltage across the inductance L2 may be substantially equal to that across the transceiver. It is evident, therefore, that the receiver amplifier is substantially protected from the full voltage of the driving unit, and these features together with the selective tuning of the impedance L2 across the receiver amplifier are instrumental in providing an efilciently operating circuit. When the system disclosed in the system is used for transmission, the circuit including L1, C1 and L2 and the projector l are so proportioned that series resonance is established across LlCl which means that the full voltage of the generator or driving unit is impressed in series across the projector and inductance L2. If, as stated above, the voltage across L2 may be 40% of the voltage across the receiver and there are 100 volts'impressed across the transceiver, then there would be 40 volts across the inductance L2 and therefore the receiver amplifier does not bear the shock of the full voltage across the projector. When the system is used for reception of the signal which the projector has already sent out for which the system is primarily designed to be used, the receiver signal being tuned to series resonance for L1 and C1, the entire voltage appearing across the projector will be impressed across the inductance L2.

' Having now described my invention, I claim: 1. In a system for measuring distance, means for transmitting a short compressional wave impulse, means for picking up said impulse after reflection from the object whose distance is to be measured, said pickup and emitting means being the same, means comprising a series circuit including said pickup means, a power source for generating high frequency electric current,

capacity and inductance elements, said inductance elements having an impedance substantially less than the transmitting and receiving device, and means for amplifying and indicating the received impulse, said means being connected across said inductance, and said capacity and power source being tuned for series resonance at the frequency at which the system operates.

2. In a system for the transmission and reception of compressional waves, a series circuit including a coil of substantially negligible resistance adapted to have a high frequency current impressed upon the coil, a compressional wave transmitting and receiving device and separate capacities and inductances having substantially negligible resistance, forming a series circuit, the capacities and coil being balanced for the high frequency current impressed upon the coil, and an amplifying unit shunted across such inductances, the impedance of such inductances being substantially less than the impedance of the transmitting and receiving device.

' 3. In a system for the transmission and reception of compressional Waves, a series circuit including a transceiver, a coil of substantially negligible resistance adapted to have a high frequency current impressed upon the coil, separate inductance and capacity elements also having substantially negligible resistance, and a receiving amplifier unit connected across said inductive element, such coil and condenser being tuned to resonance for the frequency at which the system is to operate, the impedance of said inductive element being substantially less than the impedance of the transmitting and receiving device.

4. In a system for distance finding a series circuit including a coil of substantially negligible resistance adapted to have a high frequency current impressed upon the coil, a transmitting and receiving unit, means for receiving and indicating the impulse picked up by said transmitting and receiving units, said receiving circuit including in series a capacity of negligible resistance and an inductance also of negligible resistance balanced at resonance with each other at the frequency impressed, and said receiving and indicating means being connected across said inductance, the impedance of said inductance being substantially forty per cent of the impedance of the transmitting and receiving device,

5. In a system for the transmission and reception of compressional waves, a series circuit including a plurality of inductances, a capacitance and an electromechanical energy interchanging device, the capacitive reactance and the inductive reactance of one of said inductances being substantially equal in magnitude at the frequency at which the said device is designed to operate and amplifying means connected in circuit with the remaining of the aforesaid inductances which is substantially less in magnitude than the inductance having a reactance substantially equal to that of the capacitance reactance.

6. In a system for the transmission and reception of compressional waves, a series circuit including therein, a transceiver, a receiver amplifier input element, a coupling element through which a high frequency power supply is furnished to the transceiver for transmitting and a capacitance, the said coupling element and capacitance being series tuned to resonance for the transmitting frequency whereby when the series circuit is operating as a transmitting circuit only a part of the impressed electromotive force will be impressed on the amplifying'circuit, while when it is operating as a receiving circuit all of the electromotive force developed by the transceiver will be impressed upon the amplifying circuit.

BERTRAM M. HARRISON. 

